JPS63305581A - Oscillation wavelength variable type semiconductor laser device - Google Patents

Abstract

PURPOSE:To enlarge a variable range of oscillation wavelengths, by using a beam deflection part to make beams in a laser element part become incident on an arbitrary position in a wavelength selection part, where e diffraction grating is located as a distribution reflector, so that its effective refractive indexes are serially changed perpendicularly to the incident direction of laser beams. CONSTITUTION:A wavelength selection part 71, where a diffraction grating is located, is disposed in advance so that its effective refractive indexes are serially varied perpendicularly to the incident direction of laser beams. A serial range of the effective refractive indexes is set to include a desired value of the range and to be larger than that of the refractive index obtained from a plasma effect. A beam deflection part 61 is used to make beams in a laser element part 51 become incident to a region of the wavelength selection part 71 where an arbitrary effective refractive index is indicated. Beams made incident to a certain part of the wavelength selection part 71 are oscillated at only a Bragg wavelength according to the effective refractive index on the part. Hence the wavelengths can be made variable within a range in degree of at least a gain spectral width of the laser, in accordance with the effective refractive indexes within a serial range of those indexes in the wavelength selection part 71.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a semiconductor laser device suitable for use as a light source in coherent optical communication or wavelength multiplexed optical communication, and particularly relates to a semiconductor laser device that oscillates at a single wavelength and that oscillates at a single wavelength. It is used in a semiconductor laser device that can change the wavelength.

(Prior Art) There are great expectations for optical communication as a powerful means of information transmission. In order to make such optical communications popular, a suitable light source is required, and a semiconductor laser is very suitable for this light source.

Incidentally, there are various optical communication systems, and among these, for example, coherent optical communication requires a semiconductor laser that oscillates at a specific wavelength. Furthermore, multiplex optical communication requires a plurality of semiconductor lasers whose oscillation wavelengths are slightly different from each other. Although it is possible to manufacture each of these semiconductor lasers individually for each oscillation wavelength, it is extremely difficult to obtain only semiconductor lasers that oscillate at the desired wavelength with a high yield, and The oscillation wavelength of semiconductor lasers exhibits some variation; therefore, the production yield greatly determines how many semiconductor lasers having a desired oscillation wavelength can be obtained.

In the above-mentioned case, if the semiconductor laser itself has a variable oscillation wavelength even after manufacturing, it would be advantageous in various ways, including ease of manufacturing. Therefore, research into semiconductor lasers with tunable oscillation wavelengths has been conducted for some time.

As a conventional semiconductor laser of this type, for example, the literature (OFC/IOC (OFC/100C))
-87 Technical Diquest (1987
) The wavelength tunable DBR (D
istributed BraqqBeflector
) There is a laser.

FIGS. 3(A) and 3(B) are a plan view and a side view schematically showing the schematic structure of the semiconductor laser disclosed in this document. A conventional semiconductor laser will be briefly explained with reference to these figures.

This semiconductor laser includes, on the same substrate 11, a laser element section 21 for emitting light, a phase control section 31, and an 088 section 41 having a diffraction grating with continuous irregularities.

The laser element section 21 includes a waveguide layer (InGaAsP layer) 23, a buffer layer (InP layer) 25, and an active layer (InGaAs layer) 27 on the substrate 11 from the substrate side.

Further, the optical waveguide layer 23 and the buffer layer 25 extend through the phase control section 31 to the 08 day section 41. A diffraction grating (waveform) 43 having repeated depressions and depressions is formed at the interface between the leading wave layer portion of the 088 portion 41 and the substrate 11 . Further, on the region of the buffer layer 25 corresponding to the laser element section 21, an I
An InP layer 29b is provided on a region of the nP layer 29a corresponding to the phase control section 31 of the buffer layer 25, and an InP layer 29c is provided on a region corresponding to the 088 section 41 of the buffer layer 25.

In a semiconductor laser having such a structure, light generated in the laser element section 21 is guided by the optical waveguide layer 23 and
41 and is reflected by the diffraction grating 43.

At this time, the period of the unevenness of the diffraction grating 43 is set to Δ, and the effective refractive index of the portion belonging to the 088 section 41 of the optical waveguide layer 23 is n.
5ff, the reflectance becomes large only for the light at the Bragg wavelength determined by λ8=2・n off ・△,
Therefore, this semiconductor laser oscillates only at a wavelength of λ8 (distributed reflection laser). Here, when a current is passed between the InP layer 29c of the 088 portion 41 and the substrate 11, the refractive index of the crystal in this portion changes due to the plasma effect, and as a result, the effective refractive index n off of this portion changes. When n and ff change, λe changes, and as a result, a wavelength tunable semiconductor laser is realized.

However, simply changing the current flowing through the 8th part 41 will result in a discontinuous change in wavelength, so the phase control part 3 provided between the laser element part 21 and the 08th part 41
A current is passed between the InP layer 29b of No. 1 and the substrate 11 to completely change the phase of the light from the laser element section 21 and the light from the DLR section 41, thereby making it possible to continuously change the oscillation wavelength. .

According to this conventional oscillation wavelength tunable semiconductor laser, 5
．． The oscillation wavelength could be changed continuously over a wavelength width of 8 nm.

(Problems to be Solved by the Invention) However, in the conventional semiconductor laser as explained using FIG. There was a problem that the width could not be made larger than a certain width.

In other words, when a current is passed through the 088 portion 41, the injected carriers are confined in the InGaAsP optical waveguide layer 23 because the bandgap of the InP layer is larger than the bandgap of the InGaAs1 layer 23 serving as the leading wave layer 23. , carriers increase and a plasma effect occurs. However, when the carrier density exceeds a certain value, carriers begin to flow out of the optical waveguide layer 23, and even if the injection current is increased further, the carrier density will not increase.

Since carrier density saturation means that refractive index change also saturates, there is a limit to the wavelength tuning range when using the plasma effect.

This invention has been made in view of the above-mentioned points, and therefore, an object of the invention is to increase the variable width of the oscillation wavelength compared to conventional semiconductor lasers that change the oscillation wavelength by utilizing plasma effects. An object of the present invention is to provide a tunable oscillation wavelength semiconductor laser device at which can perform the following steps.

(Means for Solving the Problems) In order to achieve this object, the oscillation wavelength tunable semiconductor laser device of the present invention includes a laser element portion, a diffraction grating as a distributed reflector (DBR), and has the following features: A wavelength selection section whose effective refractive index changes continuously in a direction perpendicular to the direction of incidence of the laser beam, and the light emitted from the laser element section described above is made incident on an arbitrary position with respect to the wavelength selection section described above. It is characterized by comprising a light deflection section.

(Function) According to the tunable oscillation wavelength semiconductor laser device of the present invention,
In addition to having a diffraction grating, a wavelength selection section whose effective refractive index changes continuously in a direction perpendicular to the incident direction of the laser beam is provided in advance. The continuous range includes the desired effective refractive index value.
However, the refractive index adjustment can be easily set to a wider range than the refractive index adjustment obtained by the plasma effect.

Further, with respect to the wavelength selection section provided in this manner, the optical deflection section causes the light from the laser element section to enter a region of the wavelength selection section exhibiting an arbitrary effective refractive index. Light incident on a certain portion of the wavelength selection section oscillates only at a Bragg wavelength corresponding to the effective refractive index of that portion. Therefore, by keeping the continuous range of the effective refractive index of the wavelength selection section wide, it becomes possible to tune the wavelength within a range at least as large as the gain spectrum width of the laser, depending on the effective refractive index within this range.

(Embodiment) Hereinafter, an embodiment of the oscillation wavelength tunable semiconductor laser device N (hereinafter also referred to as semiconductor laser device) of the present invention will be described with reference to the drawings.

Note that the figures used in the following explanation are only schematic illustrations to the extent that this invention can be understood, and therefore, the dimensions, shapes, and arrangement relationships of each component are limited to the illustrated examples only. It should be understood that similar components are designated by the same reference numerals in the drawings used for explanation.

Laser 4-1 First, the structure of the semiconductor laser device of the present invention will be explained with reference to the drawings. 1(A) to 1(D) are diagrams for explaining the structure of this semiconductor laser snow making device, FIG. 1(A) is a plan view thereof, and FIG. 1(B) is a P in FIG. 1(C) is a side view as seen from the direction indicated by Q in FIG. 1, and FIG. 1(D) is a side view as seen from the direction indicated by Q in FIG. FIG.

In FIGS. 1A and 1B, 51 indicates a laser element section, 61 indicates a light deflection section, and 71 indicates a wavelength selection section. The arrangement of these is such that the optical deflection section 61 is provided between the laser element section 51 and the wavelength selection section 71, and roughly speaking, in this embodiment, these are built on a common base 50. It is.

In this example, the base 7tInP substrate is used.

First, the laser element section 51 of this embodiment will be explained.

The laser element section 51 includes an InGaAsP layer 52 as an optical waveguide layer, an InP layer 53 as a buffer layer, and an InGaAsP layer as an active layer on an InP substrate 50 from the substrate 50 side.
A layer 54 and an InP layer 55 as an upper cladding layer are sequentially laminated. Although not shown, corresponding electrodes are provided on the back surface of the InP substrate 50 and the surface of the InP layer 55, respectively. In addition, in Fig. 1 (A) and (B), 56
The groove shown by is a groove formed from the surface of the InP layer 55 to the surface of the InP buffer layer, and the side surface of this groove 56 constitutes one end surface of the laser resonator.

Further, in the case of this embodiment, the InGaAsP optical waveguide layer 52 is provided so as to extend to the region corresponding to the optical deflection section 61 and the wavelength selection section 71 of the InP substrate 50, and
The n-tuber layer 53 is provided so as to extend to a region of the InP substrate 50 corresponding to the optical deflection section 61. Then, on the InP buffer layer of the optical deflection section 61 and the I of the wavelength selection section 7I.
An InP layer 55 is provided on the nGaAsP light guide layer.

Next, the light deflection section 61 in this embodiment will be explained. This optical deflection unit 61 includes a waveguide lens 62 on the top five InP layers and a first surface acoustic wave transducer 63.
and a second surface acoustic wave transducer 64. Although details will be described later, the laser light emitted from the laser element section 51 is deflected by acoustic flag diffraction using 63.64% of these first and second surface acoustic wave transducers. And both transducers 63°64
By changing the driving conditions, the laser beam can be deflected arbitrarily.

With reference to FIG. 2, the arrangement of the optical waveguide lenses and the like will be explained. Incidentally, FIG. 2 is a diagram showing the positional relationship of the optical waveguide lens 62, the first surface acoustic wave transducer 63, and the second surface acoustic wave transducer 64, and the action of this optical deflection section. 61 is a plan view showing the InP layer 55 from above.

The optical waveguide lens 62 is provided to convert the light emitted from the laser element section 51 into parallel light, and is made of, for example, InP.
It can be constructed from a suitable medium such as. The position where the optical waveguide lens is provided and the size of this lens are the position on the optical axis of the laser stripe of the laser element section 51 (the part shown by the broken line in FIG. 1(A) and numbered 57). Therefore, it is preferable that the width of the laser stripe be larger than the width of the laser stripe.

Also, the first and second surface acoustic wave transducers 62.6
3 are provided at positions such that they are located on both sides of the optical axis of the light that has passed through the leading waveguide lens 62, and in such a way that the surface acoustic waves output from both transducers are parallel to each other. It is.

Next, the wavelength selection section 71 of this embodiment will be explained.

In the wavelength selection section 71 in this embodiment, the partial surface of the InGaAsP optical waveguide layer 52 extending from the laser element 1151 corresponding to the wavelength selection section 71 has irregularities periodically in the direction of incidence of the laser beam. A distributed reflector (DBR) is processed into a repeating waveform.
A diffraction grating 72 is configured as a tedβraqq Reflector). Roughly speaking, in order to make the effective refractive index change continuously in the direction perpendicular to the direction of incidence of the laser beam, the thickness of the portion of the InGaAsP optical waveguide layer 52 corresponding to the wavelength selection section is set as shown in FIG. 1(D). As shown in FIG. 8, in the direction perpendicular to the direction of incidence of the laser beam (hereinafter sometimes referred to as the X direction);

Next, in order to deepen the understanding of the wavelength-tunable semiconductor laser device of the present invention, the operation of this drawing will be explained with reference mainly to FIGS. 1(B) and 2.

By applying predetermined high-frequency voltages to the first and second surface acoustic wave transducers 63 and 64, two surface acoustic waves are generated as schematically shown with 63a and 64b in FIG. Form and set aside.

The light emitted by the laser element section 51 is guided by the InGaAsP optical waveguide layer 52 and enters the optical deflection section 61 . At this time, the light beam diverges in the horizontal direction, but the laser light is converted into parallel light by the optical waveguide lens 62 of the light deflection section 61.

The laser beam that has become a parallel beam is a first surface acoustic wave 63 formed by a first surface acoustic wave transducer 63.
a, it is diffracted in the direction of an angle e given by θ=sin −′ (λ/2W). (However, λ indicates the wavelength of the laser beam, and W indicates the interval between the surface acoustic waves 63a.)
Here, if the interval between the second surface acoustic waves 64a formed by the second surface acoustic wave transducer 64 is equal to the interval between the first surface acoustic waves 63a, then
The laser beam diffracted by 3a is diffracted again by the same angle by the second surface acoustic wave 64a, and is eventually parallel to the previous laser beam and undergoes a distance shift in the direction indicated by X in FIG. becomes a laser beam. Generally speaking, in such a case, the first and second surface acoustic wave transducers 6
By changing the frequency of the high-frequency voltage applied to 3.64, the interval W of the surface acoustic waves changes, so the above-mentioned θ also changes, and therefore, the amount of displacement in the X direction can be set to the desired amount. become able to do.

By deflecting the laser light emitted from the laser element section 51 as described above, this laser light is transferred to the wavelength selection section 71.
It becomes possible to make the light incident on any arbitrary position. Furthermore, as already explained using FIG. . Effective refractive index no when light propagates in the leading wave layer
When the thickness of the waveguide layer changes, ff changes according to the following equation (1).

note = n2'+22d2 (n+2-n22)
/(1+2262)=(1) However, n2 indicates the refractive index of the bulk of InP, and n is the 1nGaAsP optical waveguide layer 52.
indicates the bulk refractive index of

Roughly speaking, if n and ff change, λB = 2 ” n
The Bragg wavelength λ8 determined by @ff· changes. (However, "in" indicates the Bragg wavelength, and "△" indicates the repetition period of the concave and convex portions of the diffraction grating 72.) Therefore, the semiconductor device of this embodiment has the following characteristics depending on the degree of deflection of the laser beam by the light deflection section: It becomes possible to change the oscillation wavelength.

Note that this invention is not limited only to the embodiments described above.

The structure of the laser element section 51 is not limited to that of the embodiment, but may be any other suitable structure as long as the object of the invention can be achieved.

In addition, in the embodiments, the semiconductor laser device of the present invention is constructed using an InP-based material, for example, GaAs.
Even when using similar materials, the same effects as in the embodiment can be obtained.

Further, although an example in which a surface acoustic wave transducer is used as the means for deflecting the light of the laser element section is explained, this deflection means may be constituted by other suitable means within the scope of the object of the present invention. You can also do that.

(Effects of the Invention) As is clear from the above description, according to the semiconductor laser device of the present invention, the light from the laser element portion is deflected by the optical deflection portion, as well as having a diffraction grating at the end of the distributed reflector (DLR). The laser beam can be made to enter any position of the wavelength selection section where the effective refractive index changes continuously in the direction perpendicular to the direction of incidence of the laser beam. Therefore, this device oscillates at a Bragg wavelength that corresponds to the effective refractive index at that location, and by changing the wavelength to this extent, the oscillation wavelength can be continuously varied. Roughly speaking, the effective refractive index range of this wavelength selection section can be changed to an appropriate value depending on the design.

This makes it possible to increase the variable width of the oscillation wavelength compared to conventional semiconductor lasers, which change the oscillation wavelength using plasma effects. For example, the gain spectrum width of the laser (
The oscillation wavelength can be changed within a range of about 10 to 30 nm).

[Brief explanation of drawings]

1A to 1D are diagrams for explaining the oscillation wavelength tunable semiconductor laser according to the embodiment of the present invention, and FIG.
FIGS. 3A and 3B are diagrams illustrating a conventional oscillation wavelength tunable semiconductor laser. be. 50... Base (InP substrate), 51... Laser element section 52... Optical waveguide layer (InGaAsP layer) 53...
- Buffer layer (InP layer) 54... Active layer (InGaAsP layer) 55... Upper cladding layer (InPl) 56... Groove,
57... Laser stripe 6)... Light deflection section,
62... Optical waveguide lens 63... First surface acoustic wave transducer 63a... First surface acoustic wave 64... Second surface acoustic wave transducer 64a...
・Second surface acoustic wave i-wave 7)...Wavelength selection section, 72...Diffraction grating. Patent applicant: Oki Electric Industry Co., Ltd.

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Claims (1)

[Claims] (1) a laser element section; a wavelength selection section having a diffraction grating as a distributed reflector (DBR) and whose effective refractive index changes continuously in a direction perpendicular to the incident direction of the laser beam; and the laser element section; 1. An oscillation wavelength tunable semiconductor laser device, comprising: an optical deflection section that causes light emitted from the wavelength selection section to enter an arbitrary position with respect to the wavelength selection section.